Intervertebral space implant for use in spinal fusion procedures

ABSTRACT

An implant assembly  10  is provided for surgical implantation into an intervertebral space S, such as for stabilization of vertebrae V adjacent the intervertebral space S during a spinal fusion procedure. The implant assembly  10  includes a primary segment  20  separate from a secondary segment  60 . These segments  20, 60  are elongate and of sufficiently small cross-section that they can be implanted posteriorly in a minimally invasive manner. The segments  20, 60  preferably have a rectangular cross-section so that they can be inserted on a side into the intervertebral space S and then rotated into a maximum height orientation to widen the intervertebral space S. The segments  20, 60  interlock together at an intersection there between. The primary segment  20  preferably includes a tunnel  30  and the secondary segment  60  preferably includes a neck  70  with the tunnel  30  and neck  70  sized complementally so that the segments  20, 60  stabilize each other where they intersect with the neck  70  within the tunnel  30 . The entire implant assembly  10  is thus provided which both widens and supports the intervertebral space S and is sufficiently rigid to provide adequate support for the intervertebral space S as the vertebrae V are fusing together. The segments  20, 60  are fitted with height expansion systems which can be accessed after implantation of the segments  20, 60  so that height of the segments  20, 60  can be further increased, particularly at distal ends  26, 66  of the segments  20, 60 , such that the intervertebral space S can be provided with a desirable amount of lordosis.

FIELD OF THE INVENTION

The following invention relates to implants which are configured to beplaced within an intervertebral space between adjacent spinal vertebraeafter a disk has been removed from the space and to facilitate fusion ofthe vertebrae together. More particularly, this invention relates toimplants which can be implanted posteriorly in either a minimallyinvasive or open manner and spread vertebrae adjacent the intervertebralspace away from each other to recreate the lumbar lordosis and supportthe vertebrae while they fuse together.

BACKGROUND OF THE INVENTION

Spinal fusion procedures are known as an effective treatment for certainspinal conditions. In general, such spinal fusion procedures may involveremoval of a disk within an intervertebral space between two adjacentvertebrae. After the disk has been removed an implant can be locatedwithin the intervertebral space to push the vertebrae apart. By pushingthe vertebrae apart, ligaments and other body structures surrounding thevertebrae are placed in tension and tend, along with the implant, tosecurely hold the two vertebrae in fixed position relative to eachother. It is important to restore as much as possible the height of theintervertebral space. It is also important to restore the angle or“lordosis” of the intervertebral space. Finally, fusion material isplaced within the intervertebral space which induces bone growth withinthe intervertebral space, effectively fusing the two vertebrae togetherwith the implant typically remaining embedded within this fused vertebracombination.

Placement of the implant within the intervertebral space is accomplishedin one of two general ways. First, the intervertebral space can beaccessed anteriorly by performing abdominal/thoracic surgery on thepatient and accessing the intervertebral space from a front side of thepatient. In this anterior procedure major abdominal/thoracic surgery istypically involved. However, the intervertebral space can be generallyaccessed anteriorly, such that the risk of injury to the nerves isgenerally reduced and the surgeon has greater flexibility in positioningthe implant precisely where desired.

Second, the implant can be inserted posteriorly. Direct posterior accessto the intervertebral space requires moving the spinal nerves within thespinal canal towards the midline and can result in nerve injury orscarring. Implantation in the intervertebral space can also be accessedfrom a location spaced to the left or right side of the spinal columnand at an angle extending into the intervertebral space. This approachavoids the spinal canal. A minimally invasive method using smallincisions can be used but is must be carefully performed to avoidsensitive spinal structures. Additionally, implants of a smaller sizeare typically required due to the small amount of clearance betweenvertebral structures. Hence, the amount of spreading of the vertebraewith a posterior implant is often less than adequate. Additionally,portions of the vertebrae typically need to be at least partially carvedaway to provide the access necessary to insert the implants posteriorlyinto the intervertebral space.

Implants for the intervertebral space come in a variety of differentconfigurations, most of which are designed for anterior implantation.One known prior art implant is described in detail in U.S. Pat. No.5,800,550 to Sertich. The Sertich implant is configured to be implantedposteriorly and comes in two pieces. Two separate incisions are made oneither side of the spine and the pieces of the overall implant areinserted generally parallel to each other, but can be angled slightlyaway from a parallel orientation. The Sertich implant pieces have arectangular cross section and an elongate form. The pieces are initiallyimplanted with a lesser dimension oriented vertically so that the piecescan easily enter the intervertebral space. The pieces are then rotated90° so that the greater dimension is rotated to vertical, tending tospread the vertebrae vertically to enlarge the intervertebral space.

The implant taught by Sertich is not entirely desirable. Because theSertich implant involves two entirely separate pieces, they do notstabilize each other in any way and hence provide a less than idealamount of vertebral stabilization. Additionally, the relatively parallelangle at which they are implanted typically requires removal of portionsof the vertebrae and retraction of the spinal nerves to properly implantthe pieces of the Sertich implant. If the two pieces of the implant areangled more towards each other, they tend to decrease further in thestability that they provide to the vertebrae. Also, the Sertich implantpieces have a size which requires a relatively large incision to insertinto the intervertebral space.

Accordingly, a need exists for a posteriorly placed intervertebral spaceimplant which has a small cross-sectional profile at insertion and yetcan provide a large amount of displacement between adjacent vertebraeonce placed. The implant must expand sufficiently far apart to restorethe height of the intervertebral space and act substantially as a singlerigid structure within the intervertebral space after implantation iscompleted. Such an invention would additionally benefit from beingcapable of having a greater height in an anterior region such thatlordosis can be achieved in an amount desired by the surgeon with ananterior side of the intervertebral space larger than a posterior sideof the intervertebral space.

SUMMARY OF THE INVENTION

This invention is an intervertebral space implant which is configured tobe implanted posteriorly in a minimally invasive or open surgicalprocedure. The implant includes two separate segments including aprimary segment and a secondary segment. The primary segment and thesecondary segment enter the intervertebral space through separateincisions on either side of the spine and along paths which intersectwithin the intervertebral space. To enhance a spreading of theintervertebral space with the implant, the segments have a heightbetween a bottom surface and a top surface which is greater than alateral width. The segments can thus be introduced into theintervertebral space with the top and bottom surfaces spaced laterallyfrom each other and then be rotated 90° so that the top surface is abovethe bottom surface and a height of the segments is maximized.

Portions of the primary segment and the secondary segment adjacent wherethe segments intersect are removed to allow the segments to lie in asubstantially common plane. Preferably, the primary segment includes atunnel passing laterally through the primary segment near a midpointthereof. The secondary segment is provided with a neck near a midpointthereof which has a lesser height than other portions of the secondarysegment. The tunnel is sized so that the secondary segment can passthrough the tunnel in the primary segment and then be rotated with theneck of the secondary segment within the tunnel of the primary segment.

After the secondary segment has been rotated the two segments areinterlocking together in a crossing pattern forming the implant assemblyof this invention. Hence, the implant assembly of this inventionprovides the advantage of having a relatively low profile for insertionposteriorly in a minimally invasive manner and yet results in an overallimplant assembly which has separate segments interlocking together toform a single substantially rigid implant assembly to maximizestabilization of the vertebrae adjacent the intervertebral space.

Additionally, the segments are formed in a manner which facilitatesheight expansion of the segments after implantation, especially atdistal ends of the segments. Such additional height expansion furtherstabilizes vertebrae adjacent the intervertebral space and provideslordosis to the intervertebral space.

Specifically, the primary segment is preferably formed with a topstructure separate from a bottom structure which pivot relative to eachother, such as about a hinge. A passage passes between the top structureand the bottom structure. A shim can pass along the passage and cause adistal end of the primary segment to be expanded in height when the shimenters a tapering end portion of the passage. The distal end of theprimary segment is thus expanded in height to an extent desired by asurgeon to provide a desirable amount of “lordosis” for the spinalfusion procedure.

Similarly, the secondary segment is preferably formed from a top jaw anda bottom jaw which can pivot relative to each other, such as about ahinge. A bore passes between the top jaw and the bottom jaw and a wedgeis caused to move within the bore in a manner causing the top jaw andthe bottom jaw to be spaced apart and causing a height of the secondarysegment to be increased at a first distal end of the secondary segment.

The insertion of the segments themselves as well as the movement ofshims and wedges within the segments to enhance their height is allaccomplished through a small posterior incision. A variety of differenthinge arrangements, shim and wedge arrangements and other structuralvariations are provided for the segments of the implant assembly.

OBJECTS OF THE INVENTION

Accordingly, a primary object of the present invention is to provide animplant for an intervertebral space which can be implanted posteriorlyand still provide a substantially rigid implant assembly for spreadingand stabilization of the vertebrae adjacent the intervertebral space.

Another object of the present invention is to provide an implantassembly having separate segments which are as low profile as possibleso that posterior implantation can be accomplished in as minimallyinvasive a surgical procedure as possible.

Another object of the present invention is to provide an implantassembly for an intervertebral space which is initially entered into theintervertebral space in separate segments which are later interlockedtogether.

Another object of the present invention is to provide an intervertebralspace implant assembly which can be adjusted in height to maximize asize of the intervertebral space generally and to allow for selectiveheight adjustment within different portions of the intervertebral space,to provide a surgeon with a maximum amount of flexibility in positioningvertebrae adjacent the intervertebral space as precisely as desired.

Another object of the present invention is to provide an implantassembly which can be located within an intervertebral space with littlerisk of damage to sensitive surrounding tissues.

Other further objects of the present invention will become apparent froma careful reading of the included drawing figures, the claims anddetailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view of a human spine with an intervertebralspace containing the implant assembly of this invention.

FIGS. 2-5 are top plan views taken along line 5—5 of FIG. 1 illustratingthe four basic steps involved in the implantation of the implantassembly of this invention.

FIG. 6 is a side elevation view of a primary segment of the implantassembly with hollow interior details shown in broken lines.

FIG. 7 is a top plan view of that which is shown in FIG. 6.

FIG. 8 is a proximal end elevation view of that which is shown in FIG.6.

FIG. 9 is a full sectional view of that which is shown in FIG. 6 andwith a guide wire and shim of this invention shown entering a passagewithin the primary segment to expand a height of the primary segmentadjacent a distal end of the primary segment.

FIG. 10 is a full sectional view of that which is shown in FIG. 9 afterthe shim has been fully advanced into the passage of the primary segmentof this invention so that the height of the distal end of the primarysegment has been enhanced.

FIG. 11 is a full sectional side elevation view of a secondary segmentof the implant assembly of this invention along with one form of a toolutilized to enhance a height of a distal first end of the secondarysegment of the implant assembly of this invention.

FIG. 12 is a top plan view of that which is shown in FIG. 11 withinterior details shown with broken lines.

FIG. 13 is a proximal second end view of that which is shown in FIG. 12.

FIG. 14 is a full sectional view of that which is shown in FIG. 11 aftera wedge has been fully advanced to enhance a height of the distal firstend of the secondary segment.

FIG. 15 is a top plan view of a tongs identifying one form of toolutilizable to implant the primary segment or the secondary segment ofthis invention.

FIG. 16 is a side elevation view of an alternative embodiment of thatwhich is shown in FIG. 6 showing an offset hinge.

FIG. 17 is a proximal end view of that which is shown in FIG. 16.

FIG. 18 is a proximal end view of a second alternative embodiment of theprimary segment of this invention.

FIG. 19 is a side elevation view of a third alternative embodiment of aprimary segment of the implant assembly of this invention with interiordetails shown with broken lines.

FIG. 20 is a distal end view of that which is shown in FIG. 19.

FIG. 21 is a side elevation view of that which is shown in FIG. 19 afterfull advancement of an alternative shim for use with the thirdalternative primary segment of the implant assembly of this invention.

FIG. 22 is a full sectional side elevation view of a fourth alternativeembodiment of a primary segment of the implant assembly of thisinvention showing a guide wire with both a shim advanced past a tunnelin the fourth alternative primary segment and a proximal shim andexpanding hinge to allow height expansion of a proximal end of thefourth alternative primary segment of the implant assembly of thisinvention.

FIG. 23 is a full sectional side elevation view of that which is shownin FIG. 22 after insertion of the proximal shim of this embodiment intoa proximal recess to enhance the proximal height of the fourthalternative primary segment of the implant assembly of this invention.

FIGS. 24-27 are sectional and side elevation views of an expanding hingeof the fourth alternative primary segment of the implant assembly ofthis invention revealing in detail the various stages in the operationof this expanding hinge.

FIGS. 28-30 are top plan views of alternatives of the implant assemblyof this invention showing how various beveled surfaces and reliefnotches can be provided adjacent the tunnel in the primary segment andthe neck in the secondary segment to facilitate rotation of thesecondary segment within the tunnel of the primary segment and tofacilitate orientation of the secondary segment at an angle relative tothe primary segment other than purely a perpendicular angle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, wherein like reference numerals representlike parts throughout the various drawing figures, reference numeral 10(FIG. 1) is directed to an implant assembly for implantation into anintervertebral space S between adjacent vertebrae V after a disk D hasbeen removed from the intervertebral space S. A primary segment 20 and asecondary segment 60 are implanted along separate pathways but interlocktogether within the intervertebral space S to form a single implantassembly 10. The resulting assembly 10 securely stabilizes the vertebraeV adjacent the intervertebral space S for spinal fusion of the vertebraeV together.

In essence, and with particular reference to FIGS. 1-5, the basicdetails of the implant assembly 10 are described. The implant assembly10 includes a primary segment 20 (FIG. 2) and a secondary segment 60(FIG. 4). The primary segment 20 is elongate in form extending along aprimary axis A. The primary segment 20 is preferably higher than it iswide (compare FIG. 2 with FIG. 3), thus having a rectangularcross-section. The primary segment 20 can thus be inserted on its sideinto the intervertebral space (along arrow C of FIG. 2) and then rotatedwithin the intervertebral space (along arrow F of FIG. 3) to help spreadvertebrae V adjacent the intervertebral space S away from each other.The primary segment 20 additionally includes a tunnel 30 (FIG. 2)passing laterally through the primary segment 20.

The secondary segment 60 (FIG. 4) is elongate and has a contourgenerally similar to that of the primary segment 20. However, thesecondary segment 60 includes a neck 70 rather than the tunnel 30 of theprimary segment 20. The secondary segment 60 has a cross-sectional sizesimilar to a size of the tunnel 30. This size allows the secondarysegment 60 to be inserted along secondary axis B (in the directionidentified by arrow E of FIG. 4) through the tunnel 30 in the primarysegment 20. The secondary segment 60 can later be rotated (along arrow Gof FIG. 5) in a manner similar to the rotation of the primary segment 20so that a height of the secondary segment 60 is oriented vertically andmaximizes a spacing of vertebrae V adjacent the intervertebral space S.The segments 20, 60 interlock together to form the implant assembly 10with the segments 20, 60 stabilizing each other and allowing the implantassembly 10 to stabilize the intervertebral spaces in which the assembly10 is implanted.

More specifically, and with particular reference to FIGS. 6-10, detailsof the primary segment 20 according to a preferred embodiment of thisinvention are described. The primary segment 20 is an elongatesubstantially rigid construct formed from a top structure 22 and abottom structure 24 which are pivotably joined together, such with ahinge 25. The hinge 25 can take on many different forms to provide thebasic function of allowing the top structure 22 and the bottom structure24 to be pivoted relative to each other.

The primary segment 20 extends from a distal end 26 to a proximal end28. A guide wire stop 27 can be optionally included with the bottomstructure 24 at the distal end 26 and extend up beyond the top structure22.

The tunnel 30 passes laterally through the primary segment 20 between atop surface and a bottom surface of the primary segment 20. The tunnel30 includes a top 32 preferably substantially parallel to a bottom 34and sides 36 extending between the bottom 34 and the top 32. The tunnel30 preferably has dimensions similar to exterior dimensions of theprimary segment 20 itself, but rotated 90°. The tunnel 30 is thus sizedto allow secondary segments 60 with dimensions similar to the primarysegment 20 to pass laterally through the tunnel 30 during formation ofthe implant assembly 10 of this invention within the intervertebralspace S (FIGS. 1-5).

A passage 40 extends longitudinally within the primary segment 20 andbetween the top structure 22 and the bottom structure 24. The passage 40includes an entrance 42 at the proximal end 28 of the primary segment.The passage 40 additionally includes a roof 44 preferably substantiallyparallel to and spaced from a floor 46. Preferably, the passage 40 has aconstant cross-section from the entrance 42 to a location where thepassage 40 intersects the tunnel 30. The passage 40 preferably continuesbeyond the tunnel 30 and toward the distal end 26 of the primary segment20. However, portions of the passage 40 on a distal side of the tunnel30 preferably taper to form a tapering end 48 of the passage 40. A step49 is preferably located in the passage 40 directly adjacent the tunnel30.

The passage 40 is configured to receive a shim 50 therein. The shim 50(FIG. 9) preferably has a rectangular cross-section which generallyfills the passage 40 (FIG. 8) so that the shim does not rotate. The shim50 preferably includes a tip 52 which is of lesser height than a tail54. A central pathway 56 preferably passes through the shim 50. A guidewire 58 can be passed entirely through the passage 40 up to the stop 27(along arrow H of FIG. 9) and then the shim 50 threaded onto the guidewire 58. The shim 50 can then be easily advanced along the guide wire 58(arrow J of FIG. 9) and directed into the passage 40. When the shim 50reaches the tapering end 48 of the passage 40, with the assistance of anappropriate shim pushing tool, the shim 50 causes the top structure 22and bottom structure 24 of the primary segment 20 to be expanded awayfrom each other (about arrow K of FIG. 10) and a height of the primarysegment 20 to be enhanced at the distal end 26 of the primary segment20.

Such distal end 26 height expansion for the primary segment 20 isdesirable in many cases to provide lordosis to the intervertebral spaceS. Specifically, lordosis is a orientation for the intervertebral spaceS where an anterior edge of the intervertebral space S has a greaterheight than a posterior edge of the intervertebral space S. Suchlordosis can be provided to a varying degree depending on the desires ofthe medical practitioner. With this invention the shim 50 is advanced anamount desired through the passage 40 of the primary segment 20 toprovide an amount of lordosis which is desirable in the judgment of themedical practitioner. The segment 20 can be custom designed to providethe lordosis desired or can be variably expandable for adjustment duringimplantation.

With particular reference to FIGS. 11-14, details of a preferredembodiment of the secondary segment 60 are described. The secondarysegment 60 preferably has a general exterior contour similar to that ofthe primary segment 20. Also, the secondary segment 60 is preferablydivided into a top jaw 62 and a bottom jaw 64 which are pivotablyconnected together, such as at a hinge 65. As with the primary segment20, the hinge 65 can take on a variety of different configurations. Thesecondary segment 60 extends from a first distal end 66 to a secondproximal end 68.

The secondary segment 60 includes a neck 70 with two preferablysubstantially parallel surfaces 72 and side walls 74 extending betweenthe parallel surfaces 72 of the neck 70 and top and bottom surfaces ofthe secondary segment 60. The side walls 74 can be perpendicular to theparallel surfaces 72 (as depicted generally in FIG. 4) or can be beveled(as shown in FIG. 11). The parallel surfaces 72 are located closer toeach other than a distance between top and bottom surfaces of thesecondary segment 60. The parallel surfaces 72 need not be preciselyparallel, but benefit from having a lesser height than that of the topand bottom surfaces of the secondary segment 60 so that the neck 70 ofthe secondary segment 60 is an open region then can reside within thetunnel 30 or other open region in the primary segment 20 after rotationof the secondary segment 60 into an orientation with the top surface andthe bottom surface vertically aligned along with top and bottom surfacesof the primary segment 20 (FIG. 5). Preferably, the neck 70 is locatednear a midpoint between the distal first end 66 and the proximal secondend 68 of the secondary segment 60.

The width between lateral sides of the secondary segment 60 ispreferably similar to a height of the neck 70 and a height of the tunnel30 in the primary segment 20 for a tight fit within the tunnel 30 bothbefore and after rotation (about arrow G of FIG. 5). The hinge 25 in theprimary segment 20, general slight flexibility of the segments 20, 60and possible slight additional clearances can provide the reliefnecessary to allow the secondary segment 60 to rotate with the neck 70within the tunnel 30. Preferably, the secondary segment 60 tends to snapinto its final position so that the segments 20, 60 are securelyinterlocked together.

To provide lordosis to the intervertebral space S, the secondary segment60 is configured to allow height expansion, particularly at the distalfirst end 66. Specifically, the secondary segment 60 includes a bore 80passing longitudinally from the proximal second end 68, at least part ofthe way toward the distal first end 66. The bore 60 includes a pin 82therein which includes a threaded end 83 at an end thereof closest tothe distal first end 66 of the secondary segment 60. An access end 84 ofthe pin 82 is opposite the threaded end 83 and closest to the proximalsecond end 68 of the secondary segment 60. A wrench 85 having one of avariety of different configurations (FIG. 11) can be utilized to causethe pin 82 to rotate by interaction of the wrench 85 with the access end84 of the pin 82. Preferably, the bore 80 is slightly smaller adjacentthe proximal end 68 to keep the pin 82 from sliding toward the proximalend 68 within the bore 80.

A wedge 86 is located within a tapering recess 87 in the bore 80. Thewedge 86 is preferably cylindrical and includes a threaded holeextending perpendicularly through curving sides of the wedge into whichthe threaded end 83 of the pin 82 is located. Hence, when the pin 82 isrotated by rotation of the tool 85 (along arrow L of FIG. 11) thethreaded end 83 of the pin 82 causes the wedge 86 to travel toward thedistal first end 66 of the secondary segment 60 (along arrow M of FIG.14). As the wedge 86 travels toward the distal first end 66 and throughthe tapering recess 87, the top jaw 62 and bottom jaw 64 are spreadvertically (along arrow N of FIG. 14), enhancing a height of thesecondary segment 60.

While the primary segment 20 and secondary segment 60 are shown withunique systems for vertically expanding top and bottom portions of thesegments 20, 60, it is noted that these systems are merely one currentlymost preferred embodiments of a vertical height enhancement system forthe segments 20, 60. In fact, a variety of different systems could beutilized to enhance the vertical height of the segments 20, 60 afterimplantation.

Most preferably, the segments 20, 60 have a height between a top andbottom surface approximately twice a width between lateral sides of thesegments 20, 60. A tongs 90 (FIG. 15) can be utilized to properly placethe segments 20, 60 within the intervertebral space S (FIG. 1). Tongs 90typically have fingers 92 which have tips 93 with a width similar tohalf of the lateral width of the segments 20. In this way, the segments20, 60 could be grasped on lateral sides with the tips 93 of the fingers92 of the tongs 90 and the segments 20, 60 can be advanced through atubular cannula with the tubular cannula having a diameter similar to aheight of the segments 20, 60 between top and bottom surfaces of thesegments 20, 60. The tongs 90 might include a pivot 94 with handles 96at ends of the tongs 90 opposite the fingers 92 for releasably graspingthe segments 20, 60.

Alternatively, the segments 20, 60 could be grasped at their proximalends 28, 68 through an appropriate attachment mechanism inboard of thetop and bottom surfaces and lateral surfaces of the segments 20, 60 sothat the tongs 90 or other placement tool would not add to across-sectional diameter needed for the cannula through which thesegments 20, 60 would be passed.

With particular reference to FIGS. 16 and 17, details of an alternativeoffset hinge 102 are described. Such an offset hinge 102 is shown on afirst alternative primary segment 100. However, the offset hinge 102could similarly be located on a secondary segment such as a modificationof the secondary segment 60 (FIGS. 11-14). The offset hinge 102advantageously allows a single pintle to pass through all leaves of theoffset hinge 102 (FIG. 17). The offset hinge 102 thus avoids thenecessity of two partial pintles on opposite sides of a passage 40 (FIG.8) or bore 80 (FIG. 13). Otherwise, the alternative primary segment 100of FIGS. 16 and 17 is similar to the primary segment 20 of the preferredembodiment of the implant assembly 10 of this invention.

FIG. 18 shows a second alternative primary segment 110 featuring a splithinge 112. This split hinge 112 on the second alternative primarysegment 110 is generally similar to the hinge 25 of the primary segment20 of the preferred embodiment (FIG. 8). However, the overlapping leavesplace the pintles of the split hinge 112 in a slightly differentposition. The second alternative primary segment 110 and split hinge 112of FIG. 8 illustrate one of the many different hinge configurationswhich the segments 20, 60 of the implant assembly 10 of this inventioncan have to effectively allow top and bottom portions of the segments20, 60 to move relative to each other.

While the material forming the segments 20, 60 would typically be someform of surgical grade bio-compatible stainless steel or other material,it is conceivable that the material forming the segments 20, 60 could bea form of hydrocarbon polymer or other plastic material, or a metallicmaterial which has some appreciable flexibility characteristics. If thesegments 20, 60 are made from such materials or can be machined to havesufficiently thin connection between the top and bottom portions of thesegments 20, 60, the hinges 25, 102, 112 of the various embodiments ofthis invention could be replaced with the top and bottom portions of thesegments 20, 60 merely flexing relative to each other sufficiently toallow the height expansion at the distal ends 26, 66 of the segments 20,60 so that an appropriate amount of lordosis can be provided to theintervertebral space S (FIG. 1).

With particular reference to FIGS. 19-21 details of a third alternativeprimary segment are described. This third alternative primary segment120 features an offset hinge 122 similar to the offset hinge 102 of thefirst alternative primary segment 100 (FIG. 16). The third alternativeprimary segment 120 additionally includes undulating overlappingtapering surfaces 124 for portions of the top and bottom structures ofthe third alternative primary segment 120 adjacent the distal end. Theseundulating overlapping tapering surfaces 124 can be spread apart bylongitudinal advancement of a first alternative shim 126 which ispreferably cylindrical and as wide as the entire segment 120. As thefirst alternative shim 126 is advanced (along arrow P of FIG. 19) itpasses through a series of steps corresponding with different stages oflordosis which can be provided to the intervertebral space S (FIG. 1).

Because the tapering surfaces 124 undulate, a series of locations areprovided where the first alternative shim 126 can come to rest. Varyingdegrees of height adjustment corresponding to various different degreesof lordosis can thus be provided to the intervertebral space S (FIG. 1).The first alternative shim 126 can be advanced by being pushed alongthrough an access passage 128 with any appropriate form of pushing tool,or could be advanced with a threaded pin similar to the advancement ofthe wedge 86 along the pin 82 of the secondary segment 60 of thepreferred embodiment.

Because the tapering surfaces 124 overlap, a greater amount of heightincrease at the distal end of the third alternative primary segment 120is provided (see FIG. 20). This third alternative primary segment 120height magnification system could be fitted on an alternative secondarysegment having a neck rather than a tunnel in a relativelystraightforward fashion due to the relatively low profile passage 128which could pass through a neck without compromising a strength of theneck in such an alternative secondary segment. Hence, this heightmagnification system is merely illustrated in the context of primarysegment for convenience, but could be equally well incorporated into asecondary segment.

With particular reference to FIGS. 22-27, details of a fourthalternative primary segment are described. The fourth alternativeprimary segment 130 is configured to allow height adjustment both at adistal end of the fourth alternative primary segment 130 and at aproximal end of the fourth alternative primary segment 130.Specifically, the top and bottom portions of the fourth alternativeprimary segment 130 are preferably joined together with an expandinghinge 132.

Function of the expanding hinge is shown in detail in FIGS. 24-27. Theexpanding hinge 132 includes two separate pintles 134 on opposite sidesof a longitudinal passage extending through the fourth alternativeprimary segment 130. The pintles 134 reside within slots 136. Hence, theexpanding hinge 132 allows both rotation and vertical expansion (alongarrow R of FIGS. 25 and 26) while still holding the top and bottomportions of the fourth alternative primary segment 130 together.

A longitudinal passage passing through the fourth alternative primarysegment includes a proximal recess 140 near a proximal end of the fourthalternative primary segment 130. A proximal shim 142 can be advancedalong a guide wire in a manner similar to the advancement of the shim 50of the primary segment 20 of the preferred embodiment. The proximal shim142 is preferably configured with a contour matching that of theproximal recess 140. Hence, as the proximal shim 142 is advanced intothe passage (along arrow Q of FIG. 22), the proximal shim 142 expandsthe top and bottom portions of the fourth alternative primary segment130 away from each other until the proximal shim 142 rests within theproximal recess 140.

As an alternative to providing the proximal recess 140, the proximalshim 142 could merely have a tapering contour (shown in FIG. 22) and thefriction between tapering surfaces of the proximal shim 142 and upperand lower surfaces of the pathway within the fourth alternative primarysegment 130 could allow the proximal shim 142 to remain in a positionwhere it has been advanced unless specific forces are applied to theproximal shim 142.

As shown in FIG. 22, a shim similar to the shim 50 of the preferredembodiment would first be advanced along the guide wire into thetapering end of the passage within the fourth alternative primarysegment 130. The proximal shim 142 would then be advanced into thepassageway. Hence, the fourth alternative primary segment 130experiences height magnification both adjacent a distal end and adjacentthe proximal end of the fourth alternative primary segment 130. Theproximal shim 142 could similarly be used with an expanding hinge 132fitted into the proximal second end 68 of the secondary segment 60 togive the secondary segment 60 proximal end 68 height adjustability.

FIG. 28 shows a fifth alternative primary segment 150 which uniquelyincludes beveled tunnel sides 152. These beveled tunnel sides 152 allowa second alternative secondary segment 155 to pass through the tunnel ina non-perpendicular direction. Specifically, the secondary segment 155can be angled relative to the fifth alternative primary segment 150 byan angular amount (arrow X of FIG. 28) which can be less than or greaterthan 90°, rather than only exactly 90°. Angle X in FIG. 8 is shown atapproximately 60° but could be reduced to as little as 45° or less andstill allow the secondary segment 155 to pass through the tunnel in thefifth alternative primary segment 150 without being blocked by thebeveled tunnel sides 152. The beveled tunnel sides 152 are shown angledapproximately 45° away from an orientation perpendicular to a long axisof the fifth alternative primary segment 150. However, the angles of thebeveled tunnel sides 152 and the angle X that the secondary segment 155shares relative to the fifth alternative primary segment 150 could beincreased or decreased depending on the needs of the medicalpractitioner for the implant assembly 10.

The second alternative secondary segment 155 preferably includes arelief bevel 156 (FIG. 28) which allows a side wall of the neck in thesecond alternative secondary segment 155 to come into contact with aside surface of the first alternative primary segment 150 after thesecond alternative secondary segment 155 has been rotated into its finalposition. The relief bevel 156 thus allows the second alternativesecondary segment 155 and the fifth alternative primary segment 150 tomore completely stabilize each other in a fully interlocking fashion sothat the implant assembly 10 stabilizes the intervertebral space S(FIG. 1) as completely as needed.

A sixth alternative primary segment 160 is shown in FIG. 29 whichincludes relief notches 162 in sides of the sixth alternative primarysegment 160 adjacent the tunnel. The relief notches 162 are analternative to the relief bevel 156 of the embodiment of FIG. 28.Specifically, FIG. 29 illustrates how either the relief bevel 156 can beprovided on the second alternative secondary segment 155 or reliefnotches 162 can be provided as in the sixth alternative primary segment160 so that complete rotation of the third alternative secondary segment164 can be achieved without the necessity of the relief bevel 156 of thesecond alternative secondary segment 155. Of course a combination of therelief bevel 156 and the relief notches 162 could be resorted to so thatabutting surfaces of the primary segment and the secondary segment couldmesh together in a manner providing stability for the overall implantassembly 10.

A fourth alternative secondary segment 170 is shown in FIG. 30 alongwith the fifth alternative primary segment 150. This implant assemblyshown in FIG. 30 is shown with the first alternative primary segment 150in section and clearly illustrating how the fourth alternative secondarysegment 170 can fit through the tunnel in the fifth alternative primarysegment 150 at an angle X (FIG. 28) other than perpendicular and berotated, about arrow T, and to the final position such as that shown inFIG. 28.

It can be seen from FIG. 30 that not all of the beveled tunnel sides 152are strictly necessary for the passage of the fourth alternativesecondary segment 170 through the tunnel in the fifth alternativeprimary segment 150. By providing the beveled tunnel sides 152 in twodirections, the fifth alternative primary segment 150 becomesreversible. However, inclusion of both beveled tunnel sides 152 wouldnot be absolutely necessary. Rather, only one beveled tunnel side 152could be provided on each side of the tunnel and other beveled tunnelsides 152 could be eliminated. Particularly, and as shown in FIG. 30,the beveled tunnel sides 152 which include reference numerals thereoncould be removed and the fourth alternative secondary segment 170 couldstill pass through the tunnel in the fifth alternative primary segment150 successfully.

Selective relief bevels 172 similar to the relief bevels 156 (FIG. 28)could be provided on some of the neck side walls, but would not need tobe on all neck side walls. The selective relief bevels 172 would come torest adjacent sides of the primary segment 150 after rotation aboutarrow T and provide enhanced stability between the segments 150, 170.

This disclosure is provided to reveal a preferred embodiment of theinvention and a best mode for practicing the invention. Having thusdescribed the invention in this way, it should be apparent that variousdifferent modifications can be made to the preferred embodiment withoutdeparting from the scope and spirit of this disclosure. For instance,while the primary segment 20 and the secondary segment 60 are describedin the preferred embodiment as being expandable, a simplified variationof this invention would not require such expandability. When structuresare identified as a means to perform a function, the identification isintended to include all structures which can perform the functionspecified.

What is claimed is:
 1. An implant for surgical placement within anintervertebral space, during a spinal fusion procedure, the implantcomprising in combination: a primary segment having an elongate formbetween a distal end and a proximal end; a secondary segment having anelongate form between a first end and a second end; and a portion ofsaid secondary segment between said first end and said second endcrossing said primary segment between said distal end and said proximalend.
 2. The implant of claim 1 wherein both said primary segment andsaid secondary segment have a height between a top surface and a bottomsurface which is greater than a width between lateral sides of saidsegments, such that rotation of said segments about a long axis from anorientation where said top surface is laterally spaced from said bottomsurface to an orientation where said top surface is above said bottomsurface results in an increase in height of both said segments.
 3. Theimplant of claim 1 wherein at least a portion of at least one of saidsegments is open sufficiently to allow the other of said segments topass at least partially through said open portion, such that saidsegments are at least partially interlocking together.
 4. The implant ofclaim 3 wherein said open portion is sufficiently large that saidsegments are substantially coplanar.
 5. The implant of claim 4 wherein aheight of said primary segment between a top surface and a bottomsurface is equal to a height of said secondary segment between a topsurface and a bottom surface with said top surface of said primarysegment coplanar with said top surface of said secondary segment andsaid bottom surface of said primary segment coplanar with said bottomsurface of said secondary segment.
 6. The implant of claim 3 whereinsaid primary segment is at least partially open between said distal endand said proximal end and said secondary segment is at least partiallyopen between said first end and said second end, said opening in saidprimary segment adjacent said opening in said secondary segment wheresaid secondary segment crosses said primary segment, such that saidprimary segment and said secondary segment are at least partiallyinterlocking together.
 7. The implant of claim 6 wherein said opening insaid primary segment is a tunnel between a top surface and a bottomsurface, said tunnel at least as large as at least a portion of saidsecondary segment between said first end and said second end, such thatsaid second segment can be located extending through said tunnel.
 8. Theimplant of claim 7 wherein said secondary segment includes a neckbetween said first end and said second end, said neck having a lesserheight between a top surface of said secondary segment and a bottomsurface of said secondary segment than a height of other portions ofsaid secondary segment adjacent said neck, said neck having a heightless than a height of said tunnel in said primary segment, such thatsaid neck of said secondary segment can be located extending throughsaid tunnel in said primary segment.
 9. The implant of claim 1 whereinsaid primary segment includes a top structure and a bottom structure,said top structure and said bottom structure movable relative to eachother, such that a height of said primary segment can be modified. 10.The implant of claim 9 wherein said primary segment includes a spacerbetween said top structure and said bottom structure, said spacer movingsaid top structure away from said bottom structure to increase a heightof said primary segment.
 11. The implant of claim 10 wherein said spaceris a shim having a tip with a lesser height than a tail, said primarysegment including a passage extending at least partially through saidprimary segment between said top structure and said bottom structure,said passage having a lesser height in a tapering region, said taperingregion closer to said distal end than to said proximal end, said shimhaving a height greater than a height of said passage at said taperingregion, such that said shim pushes said top structure away from saidbottom structure when said shim is moved through said passage into saidtapering region.
 12. The implant of claim 9 wherein said top structureand said bottom structure are hinged together at a location on saidprimary segment closer to said proximal end than to said distal end. 13.The implant of claim 12 wherein said second segment includes a top jawand a bottom jaw, said top jaw movable relative to said bottom jaw, saidtop jaw and said bottom jaw hinged together at a location closer to saidsecond end of said secondary segment than said first end of saidsecondary segment.
 14. The implant of claim 13 wherein said hinge insaid primary segment and said hinge in said secondary segment are eachexpansion hinges which allow both pivoting and vertical translation ofportions of said structures adjacent said hinge.
 15. An implant for anintervertebral space, the implant comprising in combination: a primarysegment having an elongate form between a distal end and a proximal end;a second segment having an elongate form between a first end and asecond end; a portion of said second segment between said first end andsaid second end intersecting said primary segment between said distalend and said proximal end; said primary segment including a tunnelpassing laterally therethrough between said distal end and said proximalend; said tunnel having a height less than a height of said primarysegment; said secondary segment including a neck between said first endof said secondary segment and said second end of said secondary segment;said neck having a height less than portions of said secondary segmentadjacent said neck; and said neck having a height at least as small as aheight of said tunnel in said primary segment, such that said neck insaid secondary segment can be located extending through said tunnel insaid primary segment.
 16. The implant of claim 15 wherein said neck ofsaid secondary segment is sized to allow said secondary segment torotate at least 90° about a long axis of said secondary segment whilesaid neck of said secondary segment is within said tunnel in saidprimary segment.
 17. The implant of claim 16 wherein said primarysegment includes a top structure and a bottom structure, said topstructure hingedly attached to said bottom structure at a locationcloser to said proximal end than to said distal end, and said secondarystructure having a top jaw hingedly attached to a bottom jaw at alocation on said secondary segment closer to said second end than tosaid first end.
 18. An intervertebral space implant comprising incombination: a primary segment having an elongate form between a distalend and a proximal end; a second segment having an elongate form betweena first end and a second end; a portion of said second segment betweensaid first end and said second end crossing said primary segment betweensaid distal end and said proximal end; and at least one of said segmentsat least partially open at a location between ends thereof, such thatsaid primary segment and said secondary segment are at least partiallyinterlocking where said segments cross.
 19. The implant of claim 18wherein both said primary segment and said secondary segment include anat least partially open region between ends thereof.
 20. The implant ofclaim 18 wherein said primary segment includes a tunnel passinglaterally therethrough between said distal end and said proximal end,said secondary segment including a neck between said first end and saidsecond end, said neck in said secondary segment sized sufficiently smallto pass through said tunnel in said primary segment.